The present invention is particularly adapted for making grain bin storage sheets or flooring of the type shown in copending application Ser. No. 573,969, filed Jan. 26, 1984 which is hereby incorporated by reference as if fully reproduced herein. In the aforesaid patent application there is disclosed a novel grain bin flooring which is formed from a series of corrugated plates having hooded openings in the plates through which air is blown from a blower. In grain bins of this type, the floor plates are relatively large, as disclosed in the aforesaid application, being approximately 3 feet.times.7 feet in size.
Other grain bin flooring plates such as disclosed in U.S. Pat. No. 4,073,110 are relatively narrow in that they are only approximately 7 inches in width and may extend to 30 or 40 feet in length. Such prior art grain bin flooring plates are formed with a male channel and a female channel along their respective longitudinally extending edges so that the male channel of one floor plate may be fitted into and interlocked with the channel of an adjacent plate. A method of manufacture of said sheets is shown in U.S. Pat. No. 4,418,558 which discloses the formation of the corrugations extending in a transverse direction to the longitudinal length of the flooring plates and with the slits being elongated in this transverse direction. U.S. Pat. No. 4,418,558 discloses a series of roll forming machines by which the plates are formed with the transverse corrugations and the transversely extending slits. Also, in this patent there is disclosed the method of forming the male and female channels at the time of forming of the transversely extending corrugations.
Typically, grain metal flooring plates are made of galvanized sheet metal which often is formed into a corrugated shape. The loads on the corrugated sheet metal are very substantial so that strength is an important consideration in the formation of the plates. In some instances heretofore, the plates were actually perforated with metal removal to form the aeration openings with as much as 10% of the metal being removed from the sheet. Such loss of metal has a deleterious effect on the ultimate strength of the plate. As will be explained in greater detail hereinafter, the present invention not only does not remove metal from the plate but shifts the metal upwardly and downwardly to with the openings being located at the neutral axis of the corrugations. Additionally, the plates of the present invention undergo slitting, bending and drawing which causes grain flow and cold working and increases hardness of the metal. The result has been found to significantly increase the yield strength due to cold working from for example about 45,000 psi to 55,000 psi yield.
Rather than using roll forming machines as in the aforementioned patent, the present invention is directed to the use, in this preferred embodiment, of a progressive die set which processes finished sheets as fast as the perforating or slitting operation without the use of secondary operations such as corrugating in a different machine which would involve material handling and a reduction in the efficiency of the operation.
Accordingly, an object of the present invention is to provide a new and improved method of and apparatus for making grain bin flooring plates.